1. Field of the Invention
The present invention relates to a vibration wave motor (vibration driven motor) driving control apparatus.
2. Related Background Art
In a conventional driving circuit for a vibration wave motor, the frequency of a driving frequency voltage of the vibration wave motor is limited by, e.g., a method of detecting a phase difference between the driving frequency voltage and a so-called sensor electrode for detecting a vibration state of a vibrating member of the vibration wave motor, a method of detecting the amplitude of a signal generated in a sensor electrode, or the like.
These methods include a countermeasure for preventing the rotation of the motor from being immediately stopped when the frequency of the driving voltage becomes lower than a given driving frequency in the characteristics of the vibration wave motor.
In general, a considerably high voltage is required to drive a vibration wave motor. Therefore, the following means are required. That is, a battery voltage must be boosted to a voltage level required for driving the vibration wave motor using, e.g., a DC/DC converter for boosting the driving voltage, a transformer for boosting the driving frequency voltage, or a high-voltage battery.
Therefore, when, for example, a DC/DC converter is used as a driving power supply, a large-capacity and expensive DC/DC converter must be adopted so as to assure a sufficient secondary voltage even when a supply voltage from a primary side battery drops. When a high-voltage battery is used, a large-capacity and expensive battery must also be used so as to supply a sufficient electric power to the vibration wave motor.
Therefore, when a power supply having sufficient performance cannot be used due to limited cost or space, the following problem is posed. When the output voltage of the vibration wave motor driving power supply drops due to a decrease in input voltage or an increase in load, the rotation speed of the vibration wave motor is decreased. In order to compensate for the decrease in rotation speed of the motor, when the frequency is swept or shifted toward the low frequency side, an electric power is further supplied to the vibration wave motor, and the output voltage is further decreased. As a result, the rotation of the vibration wave motor maybe undesirably stopped, due to a cause different than the above-mentioned phase difference between the driving frequency voltage and the sensor electrode. Therefore, the rotation stop phenomenon of the vibration wave motor cannot be prevented by the above-mentioned conventional control methods.